Wireless communication networks are currently in widespread use to allow mobile station users to wirelessly communicate with each other and other network entities. In one type of network, multiple stations in a particular geographic region may simultaneously communicate with a hub or base station using the same frequency band. This type of network is referred to as a self-interfering network. A code division multiple access (CDMA) network and a wideband code division multiple access (WCDMA) are both examples of self-interfering networks. Thus, the total signal power received by the base station in that frequency band may represent simultaneous transmissions from a number of the stations in the region.
For optimal network performance, especially in self-interfering networks, the transmission power of the mobile stations is carefully controlled. It can be seen that a change in transmit power by one station may affect the operation of other mobile stations, for example, requiring them to likewise change their power. In some cases, a network limit may be exceeded if a large number of mobile stations respond to one another by respectively increasing their power. This may cause the network to become unstable. To avoid this from happening, the network load may be balanced, for example, by controlling the transmission power of each mobile station to minimize its impact on other mobile stations and to accommodate for noise power in the network. The noise power is based on environmental factors, such as temperature, which change throughout the day. Thus, any technique that attempts to adjust the network load needs to account for changing noise power in the network.
One technique that is used to measure network characteristic referred to as the rise-over-thermal (RoT). The RoT is a ratio between the total power in the reverse link (Pr) and the thermal noise power (N) that is received at a receiver (i.e., base station). Thus, the rise over thermal (RoT) indicates the ratio between the total power received from wireless sources at a base station and the thermal noise.
In a WCDMA system, the shared resource in the uplink is the uplink interference. With the introduction of the enhanced uplink in WCDMA, the possibility of quickly managing the cell load is introduced by means of a fast scheduling mechanism in the base station usually termed Node B. The principle of the fast scheduling is to allow the Node B to adjust the maximum data rate a terminal is allowed to transmit with, and to reallocate the resource among users. This enables the Node B to rapidly adapt to users momentary traffic demand and interference variations. Hence, the system can be operated close to the maximum load and both user data rates and uplink capacity can be improved.
To be able to profit from the enhanced uplink scheduling function the scheduler must be provided with suitable and accurate estimates on the scheduling headroom for E-DCH. Besides the maximum load limit, the coverage limit, RoTmax and stability limit, Lmax S, the maximum scheduling headroom is depended on the cell load in the surrounding cells.
The load generated by the neighboring cells and external interference cannot be measured directly from the cell. To avoid over-scheduling of the resources, a margin is needed to account for the neighboring cell interference and external interference.
In a traditional WCDMA radio network where only speech and low data rate traffic are considered, the and where the load from surrounding cells is rather stable, a fixed margin has been used. However, with the introduction of the enhanced uplink in WCDMA, the interference variation becomes much larger. It is difficult to set a fixed margin when the load variation in the neighboring cells can be very large in a rather short time period. If a margin is set to be large enough to handle a worst-case scenario, the maximum scheduling headroom is small; and the scheduler in one cell cannot take advantage of moments when the neighboring cells are not fully loaded. However, the margin cannot be set smaller than the worst case scenario, since over-scheduling of the resources can result in power rushes and instability.
Hence, there is a problem of providing a mechanism for an improved way of operating
WCDMA networks and to optimize network performance such that the scheduler can take advantage of moments when neighboring cells are not fully loaded.